1. Field of the Invention
The present invention generally relates to vane pumping machines, and more particularly, to Invar-class iron-nickel based alloys that are used in portions of the vane pumping machine to optimize the operating performance while yielding substantial reductions in the pollution emissions of the machine. The use of Invar-class iron-nickel based alloys ensures that precise clearances are maintained for the non-contact sealing features of the machine described herein.
2. Description of the Related Art
The overall invention relates to a large class of vane pumping machines comprising all rotary vane (or sliding vane) pumps, compressors, engines, vacuum-pumps, blowers, and internal combustion engines.
This class of vane pumping machines includes designs having a rotor with slots with a radial component of alignment with respect to the rotor's axis of rotation, vanes which reciprocate within these slots, and a chamber contour within which the vane tips trace their path as they rotate and reciprocate within their vane slots. In alternate embodiments, the vanes may slide with an axial component of vane motion, or with a vector that includes both axial and radial components. The vanes may also be oriented at any angle in or orthogonal to the plane illustrated, whereby the vanes would also slide with a diagonal motion in addition to any axial or radial components. The vane motion may also have an arcuate component of motion as well. In all cases, the reciprocating vanes extend and retract synchronously with the relative rotation of the rotor and the shape of the chamber surface in such a way as to create cascading cells of compression and/or expansion, thereby providing the essential components of a pumping machine.
Within this class of vane pumping machines are internal combustion engines, which are the focus of the following discussion. Note however that the features and advantages of the later disclosed invention can be applied to any pumping machine.
Typical pollution emissions for internal combustion engines and efforts to reduce such emissions in a particular sliding vane internal combustion engine, were described in U.S. Pat. Nos. 5,524,586 and 5,836,282. By way of summary, the oxidation of hydrocarbon fuels at the elevated temperatures and pressures associated with internal combustion engines produce at least three major pollutant types:
(1) Oxides of Nitrogen (NO.sub.x); PA1 (2) Oxides of Carbon (CO, CO.sub.2); and PA1 (3) Hydrocarbons (HC) PA1 (1) lower peak combustion temperatures; PA1 (2) extended combustion duration; and PA1 (3) leaner fuel-air ratio.
Carbon dioxide (CO.sub.2) is a non-toxic necessary by-product of the hydrocarbon combustion process and can only be effectively reduced in absolute output by increasing the overall efficiency of the engine for a given application. The other major pollutants, NO.sub.x, CO, and HC, contribute significantly to global pollution and are usually the pollutants referred to in engine discussions. Other pollutants, such as aldehydes associated with alcohol fuels and particulate associated with diesel engines, contribute to global pollution as well.
Unfortunately, current production engines are not ideally suited for achieving low pollution emissions within mainstream applications such as automotives. Production engines include piston engines, Wankel rotary engines, and turbine engines, which may be divided into two fundamental categories: positive displacement engines and turbine engines.
In positive displacement engines (piston and Wankel engines) the flow of the fuel-air mixture is segmented into distinct volumes that are completely or almost completely isolated by distinct solid sealing elements (e.g., piston rings in the piston engine and rotor apex seals in the Wankel engine) throughout the engine cycle, creating compression and expansion through physical volume changes within a chamber. In the piston engine, the piston rings, which surround the piston, contact the cylinder block to seal the chamber as the piston reciprocates with the cylinder. In the Wankel engine, the apex seals of the rotor contact the stator housing as the rotor rotates within the stator housing.
Turbine engines, on the other hand, rely on fluid inertia effects to create compression and expansion, without solidly isolating chambers of the fuel-air mixture. Turbine engines, in most applications, offer three advantageous pollution emission reducing features:
Because of these three features, pollution emissions of NO.sub.x, CO, and HC are normally lower in a turbine engine than in a piston or Wankel engine. The significantly lower peak combustion temperatures--largely provided by the leaner fuel-air ratio--reduce NO.sub.x emissions by reducing the rate of formation of NO.sub.x, while the extended combustion duration and leaner fuel-air ratio reduce CO and HC emissions through oxidation of these compounds. Some turbine engines incorporate a sophisticated "Double-Cone" burner, or other such mixing devices, to allow adequate premixing of fuel and air prior to combustion, which is important to reducing NO.sub.x emissions.
Turbine engines, however, are not practical for most mainstream applications (e.g., automobiles) because of high cost, poor partial power performance, and/or low efficiency at small sizes, leaving positive displacement engines, such as the piston and Wankel designs, as the only practical alternative for these mainstream applications.
Unfortunately, commercially available piston and Wankel designs offer poor emissions performance and/or require catalytic converters to reduce emissions. Even with catalytic converters, pollutant output is substantially higher than desired. U.S. Pat. Nos. 5,524,586 and 5,836,282 describe methods of reducing pollution emissions in a positive displacement vane engine toward the scale of the aforementioned advanced turbine engines.
However, even with the above advantages, efforts continue in order to further refine and enhance the performance of the vane machine. Recall that conventional piston and Wankel engines employ contact sealing for the chamber volumes, which requires lubrication within the chambers. Such lubrication has at least two distinct drawbacks. One drawback is that since the lubricant is in the chamber, the petroleum-based lubricant itself becomes a source of pollution, both directly and indirectly, as a by-product of the combustion reaction. The second drawback is that while lubricating the contact interface between two components, the lubricant imposes undesirable temperature limitations on the chamber surface, thereby increasing heat transfer and decreasing fuel efficiency. In other words, given the temperature limits of the lubricant, the chamber surface must be kept cool enough to keep the lubricant below the breakdown temperature of the lubricant.
One means of eliminating the lubricant within the chamber is to eliminate the contact seals and replace them with non-contact or gas seals. In the context of the present invention, the gas seal may be comprised of air, compressed air, fuel-air combinations, combusted fuel-air combinations, and exhaust by-products thereof. Further study of the non-contact sealing clearances in the vane engine design highlight the importance of achieving appropriate sealing performance and reliability. However, to achieve the required non-contact sealing clearances in mainstream applications for optimum performance, the problem of the differential thermal expansion of the machine's components must be addressed and solved.
The measure of a material's susceptibility to thermal expansion is expressed as the coefficient of thermal expansion (CTE), which is the change in length per unit length of material for a one degree Centigrade change in temperature. CTE's are generally expressed as millionths of a centimeter, per centimeter, per degree Centigrade, or parts per million (ppm/.degree. C.). The CTE's of steel and aluminum typically used in pumping machines arc generally on the order of 11-20 ppm/.degree. C. The higher the CTE the greater the expansion of the material when placed under thermal load, which would obviously affect the sealing performance, sealing clearances, and reliability of the pumping machine.
The CTE for a material is especially critical for machine designs employing non-contact sealing clearances, since the non-contact sealing clearance itself is quite small, making the machine's performance quite vulnerable to small temperature changes within the machine.
Invar-class alloys are known to have remarkably low coefficients of thermal expansion (CTE). See, for example, U.S. Pat. Nos. 5,476,633 and 4,529,445. Such Invar-class alloys generally comprise nickel (30%-40%), Cobalt (0%-10%) with the remainder being iron (60%-70%). The alloys may also contain small amounts of other elements, such as manganese and silicon, to improve certain properties. See, for example, U.S. Pat. No. 4,904,447.
The two most common alloys are Super Invar and Invar 36. There are other types of Invar alloys, such as stainless steel Invar, and such Invar alloys are considered to be within the scope of the invention described hereafter. For simplicity and ease of discussion, the following description will generally focus on Super Invar and Invar 36. Super Invar generally comprises about 32% nickel (Ni), 5.5% cobalt (Co), with the remainder being iron (Fe). Super Invar has excellent dimensional stability at room temperature, but it is costly compared with other Invar alloys. Invar 36 has more practical applications since it is easier to fabricate and has a low CTE over a wider range of temperatures. Invar 36 comprises about 36% nickel (Ni) with the balance being iron (Fe).
In general, the CTE of Invar 36 can vary, depending on the composition and heat treatment, from -0.6 to +3.00 ppm/.degree. C. in the temperature range of -70.degree. C. to +100.degree. C. In most applications, the rate of thermal expansion is approximately one order of magnitude less than that of carbon steel at temperatures up to 200.degree. C. Invar 36 is used for applications where dimensional changes due to temperature variations must be minimized.
Such Invar-class alloys have been used in precision condenser plates, special joints and washers, thermostatic bimetals, and precision measurement apparatus. However, Invar-class alloys have not been used in all core components of conventional piston, Wankel or turbine engine designs. Rather, Invar-class alloys have been used mostly in portions of the engines where material stresses are low, or in engines where non-contact sealing clearances are not a concern. For example, in one conventional spark-ignition piston engine, Invar-class alloys have been used to line a small channel between a main combustion chamber and an auxiliary combustion chamber, with the small channel being formed in a cylinder head fixed onto the cylinder block. See U.S. Pat. No. 4,237,845.
Invar-class alloys are not typically used throughout conventional piston, Wankel or turbine engines for various reasons. Although Invar-class alloys have lower CTE's, they are more expensive than conventional engine materials, cannot be used in very high material stress environments, and have significant temperature limitations.
For example, Invar-class alloys are not widely used in Wankel engines because they would not substantially improve the performance of the engine, but at the same time the cost of the engine would increase undesirably. Since the Wankel engine employs contact sealing, the benefits of using a low CTE material to maintain a non-contact seal are unavailing.
Invar-class alloys are also impractical for use throughout piston engines. Again, since piston engines employ contact sealing (i.e., piston rings), the benefits of using a low CTE material to maintain a non-contact seal are unavailing. Moreover, because the power density of the piston engine is so low, the cost of the engine would increase undesirably.
Both the piston and Wankel engines require a lubricant to lubricate the contact seal between the engine components, that is, between the piston rings and the cylinder block in the piston engine, and between the apex seals on the rotor and the stator housing in the Wankel engine. The use of a lubricant undermines the benefits sought in pursuing a non-contact sealing design. More specifically, the advantages of the non-contact sealing design are fourfold: (1) eliminating the pollution-generating oil film; (2) simultaneously raising the wall temperatures beyond the breakdown temperature of the oil to thereby decrease heat transfer and increase fuel efficiency; (3) reducing mechanical friction; and (4) increasing power density by permitting an increase in tangential tip velocities, and thus flow rates.
With regard to turbine engines, the excessive operating temperatures and mechanical stresses encountered in such engines preclude the use of Invar-class alloys to any great extent.
Accordingly, an internal combustion vane engine designed for near-zero pollution and high efficiency requires non-contact sealing to eliminate the need for lubrication in the chambers or vane cells. A need exists, therefore, for a non-contact vane engine geometry which can employ and successfully exploit such Invar-class low-expansion alloys, such that the vane engine geometry and alloys provide mutual and synergistic benefits. As described hereafter, in the present invention the extremely close clearances for the non-contact sealing are achieved by using Invar-class alloys having a very low coefficient of thermal expansion. Since the unique non-contact engine design of the present invention has low internal stresses, the engine designer is not precluded from employing and exploiting the benefits of the Invar-class alloys. As a result, the low internal stress design of the engine permits the used of the rigid Invar-class alloys, while reducing or eliminating the disadvantages associated with weakness under high material stress conditions. At the same time, the non-contact sealing features of the engine are achieved by exploiting the advantageous low thermal expansion properties of the Invar-class alloys.
Another challenge to employing Invar-class alloys is to design an engine that can successfully use components comprised of the Invar-class alloys, where there is a rolling interface between the Invar component and the other components of the engine. By way of background, if an engine designer sought to employ roller bearings to reduce friction between certain components of the engine as they move relative to each other, the components should be composed of a hard material, such as hardened-steel or carbide. The roller bearings would thus have a hard surface to roll on without causing significant wear to the component. However, Invar-class alloys are relatively soft compared to, for example, the hardened-steel or carbide materials, and components manufactured from such Invar-class alloys would generally be unsuitable for use where a rolling interface is desired. A need thus exists for a vane engine whose major components are comprised of Invar-class alloys, but which employ hard bearing inserts to provide a suitable rolling surface for the bearings. Such hard bearing inserts should not, however, significantly alter the low thermal expansion properties of the Invar-class alloys.